1. Field of the Invention
The present invention relates to a high-frequency module constituting the center of, e.g., a milliwave radar mounted on a car and configured to interchange milliwaves with the outside of the car.
2. Description of the Background Art
Today, in the car electronics art, an operation support system for avoiding driver""s human errors is attracting attention. The operation support system uses a laser radar mounted on a car for radiating a laser beam toward the front of the car. By reading the resulting reflected wave, the operation support system maintains, e.g., the running speed of the car and the distance between the car and a car running ahead for thereby avoiding driver""s careless mistakes. The problem with the laser beam is that information being read is often effected by rain, fog and other weather conditions. In light of this, a milliwave ranging from 30 GHz to 40 GHz (international standard is 76.5 GHz) is recommended in place of the laser beam.
A high-frequency module, which constitutes the center of, e.g., a milliwave radar, generates a milliwave, radiates it to the outside via a waveguide, receives the resulting reflected wave from the outside, and calculates a difference between the frequency of the radiated wave and that of the received wave for thereby achieving the object. A conventional high-frequency module includes an MCM (Multi Chip Module) substrate or laminate ceramic substrate on which parts constituting high-frequency (microwave to milliwave) circuitry are mounted. Three interface substrates connect the high-frequency circuitry and waveguide. A metallic casing supports the MCM substrate and interface substrates and is formed with three waveguide holes. A cover covers the waveguide holes and forms a waveguide end cavity.
In the conventional high-frequency module described above, GND (ground) potential is connected between the MCM substrate and the interface substrates by way of GND connection wires and metallic casing, so that the microstrip line lacks continuity. As a result, if the MCM substrate and interface substrates are not accurately matched, then the characteristics of the module are degraded or the scatter is aggravated. This problem is aggravated because the plurality of interface substrates cause the positional accuracy of structural parts to critically effect the characteristics of the module, resulting in the scatter of the input and output characteristics of high-frequency signals.
Moreover, alumina-ceramic substrates constituting the interface substrates are not flexible and are therefore difficult to machine. This, coupled with the fact that the number of interface substrates is great, increases the number of assembling steps and therefore the production cost.
It is an object of the present invention to provide a high-frequency module capable of reducing the scatter of high-frequency characteristics to thereby stabilize the characteristics.
It is another object of the present invention to provide a high-frequency module capable of reducing the number of assembling steps and therefore cost.
A high-frequency module of the present invention includes a laminate ceramic layer including a first layer smaller in area than the other layers. Parts constituting high-frequency circuitry are mounted on the laminate ceramic layer. A single interface substrate is juxtaposed to the first layer and connects the high-frequency circuitry and a waveguide. A metallic casing supports the laminate ceramic substrate and interface substrate with ground held in contact. The metallic casing is formed with at least one waveguide hole. A cover covers the waveguide hole and forms a waveguide end cavity. The interface substrate is positioned on the second layer of the laminate ceramic substrate, which just underlies the first layer, at one side and protrudes from the metallic casing into the waveguide hole at the other side.